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LibC: Don't delete null check in gettimeofday

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The `nonnull` attribute may delete null checks in the generated code, as
per the [GCC documentation]:

> The compiler may also perform optimizations based on the knowledge
> that nonnul parameters cannot be null. This can currently not be
> disabled other than by removing the nonnull attribute.

Disassembling the function as compiled by GCC, we can see that there is
no branch based on if `tv` is null.  This means that `gettimeofday`
would produce UB if passed a null parameter, even if we wanted to
predictably return an error.  Clang refuses to compile this due to a
`pointer-bool-conversion` warning.

In this commit, `settimeofday` is changed as well to match
`gettimeofday`'s null argument handling.

[GCC documentation]:
https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-nonnull-function-attribute
This commit is contained in:
Daniel Bertalan 2021-08-11 10:36:08 +02:00 committed by Andreas Kling
parent 8b6397446e
commit f95a11a7da
Notes: sideshowbarker 2024-07-18 07:03:45 +09:00 
Author: https://github.com/BertalanD
Commit: https://github.com/SerenityOS/serenity/commit/f95a11a7daa
Pull-request: https://github.com/SerenityOS/serenity/pull/9339
Reviewed-by: https://github.com/alimpfard
Reviewed-by: https://github.com/dascandy ✅
2 changed files with 7 additions and 2 deletions
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4
Userland/Libraries/LibC/sys/time.h
View File

@ -23,8 +23,8 @@ struct timezone {
};
int adjtime(const struct timeval* delta, struct timeval* old_delta);
int gettimeofday(struct timeval* __restrict__, void* __restrict__) __attribute__((nonnull(1)));
int settimeofday(struct timeval* __restrict__, void* __restrict__) __attribute__((nonnull(1)));
int gettimeofday(struct timeval* __restrict__, void* __restrict__);
int settimeofday(struct timeval* __restrict__, void* __restrict__);
int utimes(const char* pathname, const struct timeval[2]);
static inline void timeradd(const struct timeval* a, const struct timeval* b, struct timeval* out)

5
Userland/Libraries/LibC/time.cpp
View File

@ -54,6 +54,11 @@ int gettimeofday(struct timeval* __restrict__ tv, void* __restrict__)
int settimeofday(struct timeval* __restrict__ tv, void* __restrict__)
{
if (!tv) {
errno = EFAULT;
return -1;
}
timespec ts;
TIMEVAL_TO_TIMESPEC(tv, &ts);
return clock_settime(CLOCK_REALTIME, &ts);